Generally, droplet jetting apparatuses for jetting (discharging) fluid in droplet shapes have been widely used in ink jet printers and recently are being developed to be applied to high value-added production industries, such as display production processing equipment, printed circuit board production processing equipment and DNA chip production processing equipment.
In ink jet printers, ink jetting apparatuses for jetting ink into droplet shapes are classified into a thermal-actuation type and an electrostatic type.
First, as shown in FIGS. 1 and 2, a thermal-actuation type ink jetting apparatus includes a manifold 22 which is provided on a base plate 10, an ink channel 24 and an ink chamber 26 which are defined by partitions 14 provided on the base plate 10, a heater 12 which is provided in the ink chamber 26, and a nozzle 16 which is formed in a nozzle plate 18 to jet an ink droplet 29′. A thermal-actuation type ink jetting apparatus having the above construction jets the ink droplet 29′ through the following operation.
The heater 12 generates heat using voltage applied thereto. Ink 29 that is contained in the ink chamber 26 is heated by the heat, so that a bubble 28 is created.
The created bubble 28 is continuously expanded, thus applying pressure to the ink 29 contained in the ink chamber 26. Hence, a droplet 29′ is jetted to the outside through the nozzle 26.
Thereafter, ink 29 is supplied from the manifold 22 into the ink chamber 26 through the ink channel 22, thus recharging the ink chamber 26.
However, in the thermal-actuation type ink jetting apparatus, ink 29 may be chemically deformed by heat generated from the heater 12 for the purpose of creating bubbles, with the result that the quality of the ink 29 deteriorates.
Furthermore, while a droplet 29′ of ink jetted from the nozzle 16 moves towards the material to be printed on, such as paper, the droplet 29′ may rapidly vary in volume due to the heat of the heater 12, thus reducing the printing quality, for example, reducing the resolution.
In addition, the thermal-actuation type ink jetting apparatus is problematic in that it is very difficult to minutely control, for example, the shape and size of the droplet 29′ jetted from the nozzle 16.
As well, due to the above-mentioned problems, it is not easy to realize a highly integrated droplet jetting apparatus.
Meanwhile, FIGS. 3 and 4 illustrate an electrostatic droplet jetting apparatus which uses an electric field, unlike the above droplet jetting apparatus.
As shown in FIGS. 3 and 4, the electrostatic droplet jetting apparatus includes a base electrode 32 and an opposite electrode 33 which face each other. Ink 31 is injected between the two electrodes 32 and 33. A DC power supply 34 is connected to the two electrodes 32 and 33.
When voltage is applied to the electrodes 32 and 33 by the DC power supply 34, an electrostatic field is formed between the two electrodes 32 and 33.
Then, Coulomb's force is applied to the ink 31 in the direction toward the opposite electrode 33.
Meanwhile, because of the surface tension and viscosity of the ink, a force repulsive to Coulomb's force is generated on the ink 31, so that the ink 31 is not easily jetted towards the electrode 33.
Therefore, to separate a droplet from the surface of the ink 31 and jet the droplet, a relatively high voltage, for example, 1 kV or more, must be applied between the electrodes 32 and 33.
Furthermore, if high voltage is not applied between the electrodes 32 and 33, droplets are irregularly jetted and a certain portion of the ink 31 is partially heated.
In detail, a temperature T1 of ink 31′ in an area S1 becomes higher than a temperature T0 of ink 31 in an area other than the area S1. Thus, the ink 31′ in the area S1 is expanded and the electrostatic field is focused on this area, so that lots of electrons collect there.
Therefore, repulsive force applied between electrons and Coulomb's force attributable to the electrostatic field are applied to the ink 31′ in the area S1. Thus, as shown in FIG. 4, a droplet is separated from the ink 31′ in the area S1 and moves towards the opposite electrode 33.
However, the electrostatic droplet jetting apparatus having the above-mentioned construction is problematic in that very high voltage, for example, 1 kV or more, must be applied to the electrodes 32 and 33 and the separate opposite electrode 33 must be provided at a position facing the nozzle. Furthermore, there is a technical limit in the realization of nano-scale patterning, which has been recently regarded as important. Recently, as the size of a device is reduced from a micro-scale to a nano-scale level, the manufacture of a nano-scale structure becomes more important. As the results of research into printing techniques for patterning nano-scale structures, there have resulted an atomic-force microscope (AFM) based method, a nanopipet deposition method, a beam-based method, a contact printing method and an electric radiation method. The above-mentioned methods make nano-scale patterning possible, but there are disadvantages in that the speed of the patterning is relatively slow and they cannot be used to pattern over a large area. Hence, a rapid printing technique that can conduct patterning in both micro- and nano-scale is required.